This invention relates to a liquid-cooled internal combustion engine with a crankcase, at least one cylinder head, at least one exhaust manifold, at least one turbocharger, at least one charge heat exchanger and at least one raw water heat exchanger, which are connected into a coolant circuit together with a coolant pump.
German patent document DE 198 10 726 A1, entitled Exhaust Gas Duct Cooled with Water, published Sep. 16, 1999, A. Kschischo and M. Rapp, inventors, discloses an internal combustion engine which includes a charge heat exchanger and a raw water heat exchanger. The cooling system of this internal combustion engine is essentially constructed in such a way that coolant flows successively through the crankcase of the internal combustion engine together with the cylinder heads, the supercharger and then the exhaust manifolds. A raw water heat exchanger is connected to the exhaust manifolds on the discharge side and, in series with the exhaust manifolds, a charge heat exchanger is incorporated into the coolant circuit. As a whole, the coolant circuit is made as a series system, the principal stress in this document being laid on the design of the exhaust manifolds with respect to coolant guidance and assembly.
It is an object of the invention to furnish a liquid-cooled internal combustion that is optimized with respect to coolant stream guidance.
According to the invention, this object is achieved by virtue of the fact that the coolant circuit downstream of the coolant pump is divided into
a) an engine cooling loop through the internal combustion engine with the crankcase and the cylinder head,
b) an exhaust loop with the exhaust manifold and the turbocharger and
c) a heat exchanger loop with the charge heat exchanger and the raw water heat exchanger
in parallel configuration, and these loops are recombined upstream of the coolant pump. This design lowers the net flow resistance of the coolant circuit relative to differently connected coolant circuits and thus reduces the danger of cavitation, among other things. Thus the coolant pump must convey the coolant against a lower differential pressure than in known coolant circuits, so that a lower net drive power is required. The invention takes its initial point of departure from a given engine cooling loop through the internal combustion engine with the crankcase and the cylinder head, and the maximum coolant quantity to be conveyed through these components is taken as a given quantity. On the basis of this quantity and the flow resistance of the components of the internal combustion engine through which the coolant flows, from inlet to discharge side, a certain differential pressure results, which in turn determines the mass flow rate of the coolant. The additional components to be cooled or, respectively, heat exchangers through which coolant is to flow, are combined into groups and, in further development of the invention, are designed in such a way that the differential pressure in these loops, namely the exhaust loop and the heat exchanger loop, is adjustable. This is accomplished by the components themselves or, if appropriate, by the respectively required tubing connections or by throttles, adjustable if appropriate, inserted into these tubing connections or the components. By virtue of this design, the differential pressure over the engine cooling loop, the exhaust loop and the heat exchanger loop comes out to the same value in each case. This insures that the necessary quantity of coolant flows through the individual loops.
In development of the invention, a coolant thermostat is inserted into the heat exchanger loop on the inlet side and controls a coolant flow through the raw water heat exchanger and a bypass around this heat exchanger. Further, the coolant stream is guided through the charge heat exchanger. By virtue of this design, a relatively large substream is led from the coolant thermostat through the raw water heat exchanger in accordance with the engine inlet temperature. There is no flow through the raw water heat exchanger during the engine warmup phase, so that the charge cooler also does not provide a cooling function. In this operating mode, the combustion air supplied to the engine is heated in the charge cooler by the coolant. In this way, the usual blue smoke of the engine in this operating mode, that is, cold start/low load, is markedly reduced or entirely avoided. When the engine is warmed up to operating temperature, a large part of the coolant of the heat exchanger, and thus cooled coolant, is supplied to the charge cooler. A powerful cooling action of the charge is achieved in this way. This guarantees a low charge temperature when the engine is in full-load operation. A further advantage of this design is that because only a substream of the total coolant stream flows through the coolant thermostat, a smaller mass-produced thermostat can be employed.
In development of the invention, a transmission oil heat exchanger is connected in parallel with the charge heat exchanger and a heating loop may be connected in parallel with the engine cooling loop, the exhaust loop and the heat exchanger loop. These features are included depending on the requirement.
In further development of the invention, the internal combustion engine is designed as a multicylinder V-type engine with two cylinder head rows and thus forms the engine cooling circuit. The exhaust loop in this design is divided into two identical loops connected in parallel. Naturally, the solution is also applicable for an in-line engine.